1. Field of the Invention
This invention pertains generally to the field of communications in oil and gas drilling operations and other similar activities in which exchange of information is required between the earth's surface and regions downhole. The invention described in this application utilizes inductive or capacitive coupling at joints between sections of pipe, impedance matching and coil (or capacitor) shielding to minimize attenuation and reflection of signal to afford effective real-time or near-real-time communications in a high-speed, robust system that conveniently integrates into current drilling practices and other downhole applications.
2. Description of the Related Art
Presently, a common mode of communicating information between downhole regions and the surface is mud-pulse telemetry. In this technique, a valve downhole opens and closes creating backpressure pulses in the mud being pumped down the drill pipe. A pressure transducer at the surface measures these pulses reading the signal from downhole. Although this method is commonly used, it suffers from low bit rate (<10 bits per second) and communications are uni-directional.
Other wireless systems such as EM or Earth Current systems that transmit through the earth have also been built, but their performance is no better than mud-pulse telemetry. These systems are also less reliable, depending on the types of formation drilled through.
There have been numerous attempts to add wire to drill pipe including the use of slip rings at joints (physical contact/connection) and inductive coupling at the joints. Active electronics at the joints including use of Hall effect sensors has been proposed. Slip rings are not robust, requiring special care while making up the joints. The inductive coupling concepts proposed previously have not resolved issues relating to of how to control/minimize reflections of the signal at the joints. Consequently, issues relating to signal attenuation continue to plague many downhole telemetry systems. Additionally, active electronics add cost and complexity to systems. For example, for 20,000 feet of drill pipe, 650 sets of electronics and batteries may be necessary using systems based on active electronics. If just one electronic package or battery fails, the whole system fails.